1. Field of the Invention
The present invention relates to a dielectric duplexer and a communication apparatus using the dielectric duplexer.
2. Description of the Related Art
Conventional filters designed for use in, for example, microwave bands are configured to have resonance lines provided on a dielectric board, a dielectric block, or the like. For example, for bandpass filters, the central frequency of a passing band, passing-band widths, attenuation-pole frequencies, and the like are designed to meet required technical specifications. As particular examples, dielectric filters designed so as to control characteristics over transient regions from passing bands to attenuation bands have been proposed by Japanese Unexamined Patent Application Publications Nos. 62-161202 and 7-321508.
Japanese Unexamined Patent Application Publication No. 62-161202 proposed an antenna duplexer configured of two bandpass filters. One of the bandpass filters has attenuation characteristics with a greater gradient in the direction from a passing band to an attenuation band on the low-band side than in the direction from the passing band to an attenuation band on the high-band side. In contrast, the other of the bandpass filters has attenuation characteristics with a greater gradient in the direction from a passing band to an attenuation band on the high-band side than in the direction from the passing band to an attenuation band on the low-band side.
Japanese Unexamined Patent Application Publication No. 7-321508 proposed a bandpass filter configured of resonators coupled by means of a concentrated-constant-type coupling element. In the bandpass filter, to increase amounts of attenuation in attenuation bands, magnetic coupling is used for interstage coupling in a low-band-side bandpass filter, and capacitive coupling is used for interstage coupling on a high-band-side bandpass filter.
In order to use each of these conventional dielectric filters as an antenna duplexer, a configuration can be such that attenuation poles are individually provided in a high band of the low-band-side bandpass filter and in a low band of the high-band-side bandpass filter. This configuration can produce attenuation characteristics which sharply change in a direction from one of the passing bands to the other one of the passing bands. However, a problem arises in that the antenna duplexer is influenced by waves (noise waves) in an adjacent frequency band: namely, in a band of higher or lower frequency than the high or low passing bands.
Accordingly, an object of the present invention is to provide a dielectric duplexer that has first and second filters passing two adjacent bands and that is not influenced by signals in bands that are adjacent to and outside the two passing bands.
Another object of the present invention is to provide a communication apparatus using the aforementioned dielectric duplexer.
To these ends, according to one aspect of the present invention, there is provided a dielectric duplexer, comprising: a first filter having a plurality of resonance lines provided on a dielectric member, for passing a lower-side band; and a second filter having a plurality of resonance lines provided on the dielectric member, for passing a higher-side band; wherein adjacent resonance lines of the first filter are coupled at their predetermined portions to each other by distributed-constant-inductive coupling, so as to generate an attenuation pole in the high-frequency side of the passing band, while adjacent resonance lines of the second filter are coupled at their predetermined portions to each other by distributed-constant-capacitive coupling, so as to generate an attenuation pole in the low-frequency side of the passing band, and wherein adjacent resonance lines of the second filter are coupled at their other portions to each other by distributed-constant-inductive coupling, so as to generate an attenuation pole also in the high-frequency side of the passing band of the second filter.
According to another aspect of the present invention, there is provided a dielectric duplexer, comprising: a first filter having a plurality of resonance lines provided on a dielectric member, for passing a lower-side band; and a second filter having a plurality of resonance lines provided on the dielectric member, for passing a higher-side band; wherein adjacent resonance lines of the first filter are coupled at their predetermined portions to each other by distributed-constant-inductive coupling, so as to generate an attenuation pole in the high-frequency side of the passing band, while adjacent resonance lines of the second filter are coupled at their predetermined portions to each other by distributed-constant-capacitive coupling, so as to generate an attenuation pole in the low-frequency side of the passing band, and wherein adjacent resonance lines of the first filter are coupled at their other portions to each other by distributed-constant-capacitive coupling, so as to generate an attenuation pole also in the low-frequency side of the passing band of the first filter.
With these features, it is possible to realize sharp attenuations not only in the higher-frequency side of the first filter that passes lower frequency band and the lower-frequency side of the second filter that passes higher frequency band, but also at the lower-frequency side of the first filter and at the higher-frequency side of the second filter, whereby influences of signals which are outside and adjacent to the two passing bands can be significantly suppressed.
The arrangement may be such that the dielectric member is a substantially rectangular parallelepiped dielectric block, and the resonance lines are constituted by inner conductors in resonator holes formed in the dielectric block, and wherein the distributed-constant-inductive coupling or the distributed-constant-capacitive coupling is implemented by determining the distance between portions of adjacent resonator holes near the open-circuit ends of the resonator holes and the distance between portions of the adjacent resonator holes near the short-circuit ends of the resonator holes.
With this arrangement, it is possible to obtain a dielectric multiplexer which is easy to manufacture and which can suppress unnecessary frequency signals outside the two passing bands, by using a single dielectric block and suitably determining the configurations of the resonator holes.
The arrangement also may be such that the dielectric member is a substantially rectangular parallelepiped dielectric block, and the resonance lines are constituted by inner conductors in resonator holes formed in the dielectric block, and wherein the distributed-constant-inductive coupling or the distributed-constant-capacitive coupling is implemented by determining the effective inductivity between portions of adjacent resonator holes near the open-circuit ends of the resonator holes and the effective inductivity between portions of the adjacent resonator holes near the short-circuit ends of the resonator holes.
With this arrangement, it is possible to obtain a dielectric multiplexer which can suppress unnecessary frequency signals outside the two passing bands, by using a single dielectric block and by suitably determining the effective inductivities at predetermined portions of the dielectric block. Thus, the characteristics of the dielectric duplexer can be determined by the outer shape of the dielectric block, and can easily be adjusted from the exterior of the dielectric block.
The arrangement also may be such that the dielectric member is a substantially rectangular parallelepiped dielectric block, and the resonance lines are constituted by inner conductors in resonator holes formed in the dielectric block, and wherein the distributed-constant-inductive coupling or the distributed-constant-capacitive coupling is implemented by determining the opposing area of the inner conductors of adjacent resonator holes near the open-circuit ends of the resonator holes and the opposing area of the inner conductors of the adjacent resonator holes near the short-circuit ends of the resonator holes.
With this arrangement, it is possible to obtain a dielectric multiplexer which can suppress unnecessary frequency signals outside the two passing bands, by using a single dielectric block and by suitably determining the regions where the inner conductors of the resonator holes are to be formed. Thus, the characteristics of the dielectric demultiplexer can be determined by partial removal of the inner conductors, and can easily be adjusted from the exterior of the dielectric block.
The arrangement also may be such that the dielectric member is a substantially rectangular parallelepiped dielectric block, and the resonance lines are constituted by inner conductors in resonator holes formed in the dielectric block, the dielectric block having conductor patterns formed on the external surface thereof and continuing from the inner conductors, and wherein the distributed-constant-inductive coupling or the distributed-constant-capacitive coupling is implemented by determining the electrostatic capacitance between portions of adjacent resonance lines near the open-circuit ends of the resonator lines and the electrostatic capacitance between the open-circuit end of the resonance line and the external conductor formed on the external surface of the dielectric block.
With this arrangement, it is possible to obtain a dielectric multiplexer which is easy to manufacture and which can suppress unnecessary frequency signals outside the two passing bands, by using a single dielectric block and by suitably designing conductor patterns on the external surface of the dielectric block. Thus, the characteristics of the dielectric multiplexer can easily be determined and adjusted by suitably determining the conductor pattern.
Alternatively, the dielectric member may be a dielectric board. In such a case, the arrangement may be such that the resonance lines are constituted by microstrip lines formed on the dielectric board, and wherein the distributed-constant-inductive coupling or the distributed-constant-capacitive coupling is implemented by determining the distance between portions of adjacent microstrip lines near the open-circuit ends of the microstrip lines and the distance between portions of the adjacent microstrip lines near the short-circuit ends of the microstrip lines.
This arrangement permits the dielectric multiplexer to be manufactured with a reduced number of production steps and, hence, at a reduced cost, because the dielectric member is formed of a board.
In accordance with another aspect of the present invention, there is provided a communication apparatus comprising: a transmitting circuit connected to an input port of the first filter of the dielectric duplexer of any type described heretofore; a receiving circuit connected to an output port of the second filter of the dielectric duplexer; and an antenna connected to a common input/output port of the first and second filters.
With these features, it is possible to obtain a small-sized, lightweight communication apparatus, by virtue of the use of the dielectric duplexer which, despite a reduced size, exhibits required characteristics.
The above and other objects, features and advantages of the present invention will become clear from the following description of the preferred embodiments when the same is read in conjunction with the accompanying drawings.